I. Field
The following description relates generally to wireless communication systems, and more particularly, but not exclusively, to frequency selective precoding that satisfies a cubic metric (CM) criteria for uplink (UL) telecommunication in an advanced telecommunication network that supports multiple-in-multiple-out (MIMO) communication in the UL.
II. Relevant Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so forth. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, Long Term Evolution (LTE) systems including E-UTRA, and orthogonal frequency division multiple access (OFDMA) systems.
An orthogonal frequency division multiplex (OFDM) communication system effectively partitions the overall system bandwidth into multiple subcarriers, which may also be referred to as frequency sub-channels, tones, or frequency bins. For an OFDM system, the data to be transmitted (i.e., the information bits) is first encoded with a particular coding scheme to generate coded bits, and the coded bits are further grouped into multi-bit symbols that are then mapped to modulation symbols. Each modulation symbol corresponds to a point in a signal constellation defined by a particular modulation scheme (e.g., M-PSK or M-QAM) used for data transmission. At each time interval that may be dependent on the bandwidth of each frequency subcarrier, a modulation symbol may be transmitted on each of the frequency subcarriers. Thus, OFDM may be used to combat inter-symbol interference (ISI) caused by frequency selective fading, which is characterized by different amounts of attenuation across the system bandwidth.
Generally, a wireless multiple-access communication system can concurrently support communication for multiple terminals that communicate with one or more base stations via transmissions on downlink and uplink. As indicated supra, the downlink refers to the communication link from the base stations to the terminals, and the uplink refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out (SISO), single-in multiple-out (SIMO), multiple-in-single-out (MISO) or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels. Generally, each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. A MIMO system also supports time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the downlink and uplink transmissions are on the same frequency region so that the reciprocity principle allows estimation of the downlink channel from the uplink channel. This enables an access point to extract transmit beam-forming gain on the uplink when multiple antennas are available at the access point.
Development of mobile wireless networks, or telecommunication networks, has been directed primarily to improving various aspects of network performance (e.g., data rates, network latency, control overhead, resource utilization, etc.) within an allocated bandwidth in order to offer subscribers a better experience and ensuing perceived quality of service when utilizing applications which demand high data throughputs. In communication systems (e.g., LTE Advanced (Release 10)), uplink (UL) spatial multiplexing of up to four layers is supported with wide-band precoding (e.g., application of a single precoding matrix per UL component carrier). In wide-band precoding, single-carrier waveform can be maintained at each antenna in a set of antennas in a user equipment (UE) and, generally, a single precoding matrix indicator (PMI) is signaled.
Advanced telecommunication networks can allow MIMO communication in the UL to attain higher data rates and increase overall network performance; however, spatial multiplexing in conventional communication typically preserves the cubic metric (CM) of single-carrier waveform and thus the CM of the transmitted waveform at each antenna in the set of antennas in the UE is the same as SIMO transmission rather than specific to MIMO communication in the UL. In addition, for frequency-selective precoding (e.g., application of different precoding matrices in different frequency bands of an UL component carrier), the transmitted waveform from one transmit antenna in the set of antennas in the UE may no longer be single-carrier waveform and thus the transmitted waveform may exhibit high cubic metric.